# -*- coding: utf-8 -*-
# @Time    : 2021/4/20 20:25
# @Author  : N
# @Email   : 
# @File    : 正整数一直输出.py
# @Software: PyCharm
import re
while True:
    a=input("请输入：")
    ret=re.findall(r"^\+?\d+$",a)
    if ret:
        print("".join(ret))
        break
    else:
        print("不是正整数")
        continue


